My Dad taught me a version of this. The words are:

Mochyn du sydd wedi marw
Dad a Mam yn crio'n arw
Wedi ei gladdu yn y berllan
Gyda'i drwyn yn sticio allan

O mor drwm y rydym ni
O mor drwm y rydym ni
Dad a Mam s'yn crio'n arw
Wedi claddu'r mochyn du



roughly translated means:

The black pig has died
Mum and Dad are crying
They buried him in the orchard
With his nose sticking out

Oh how heavy hearted we are
Oh how heavy hearted we are
Mum and Dad are crying a lot
After burying the black pig